Using `errors.As` to check for validation errors

example_test.go

@@ -1,6 +1,7 @@
 package jwt_test
 
 import (
+	"errors"
 	"fmt"
 	"time"
 
@@ -94,16 +95,22 @@ func ExampleParseWithClaims_customClaimsType() {
 
 // An example of parsing the error types using bitfield checks
 func ExampleParse_errorChecking() {
-	// Token from another example.  This token is expired
-	var tokenString = "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJmb28iOiJiYXIiLCJleHAiOjE1MDAwLCJpc3MiOiJ0ZXN0In0.HE7fK0xOQwFEr4WDgRWj4teRPZ6i3GLwD5YCm6Pwu_c"
+	var (
+		token *jwt.Token
+		ve    *jwt.ValidationError
+		err   error
+	)
 
-	token, err := jwt.Parse(tokenString, func(token *jwt.Token) (interface{}, error) {
+	// Token from another example.  This token is expired
+	tokenString := "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJmb28iOiJiYXIiLCJleHAiOjE1MDAwLCJpc3MiOiJ0ZXN0In0.HE7fK0xOQwFEr4WDgRWj4teRPZ6i3GLwD5YCm6Pwu_c"
+
+	token, err = jwt.Parse(tokenString, func(token *jwt.Token) (interface{}, error) {
 		return []byte("AllYourBase"), nil
 	})
 
 	if token.Valid {
 		fmt.Println("You look nice today")
-	} else if ve, ok := err.(*jwt.ValidationError); ok {
+	} else if errors.As(err, &ve) {
 		if ve.Errors&jwt.ValidationErrorMalformed != 0 {
 			fmt.Println("That's not even a token")
 		} else if ve.Errors&(jwt.ValidationErrorExpired|jwt.ValidationErrorNotValidYet) != 0 {

parser_test.go

@@ -4,6 +4,7 @@ import (
 	"crypto"
 	"crypto/rsa"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"reflect"
 	"testing"
@@ -325,6 +326,7 @@ func TestParser_Parse(t *testing.T) {
 
 			// Parse the token
 			var token *jwt.Token
+			var ve *jwt.ValidationError
 			var err error
 			var parser = data.parser
 			if parser == nil {
@@ -361,8 +363,7 @@ func TestParser_Parse(t *testing.T) {
 				if err == nil {
 					t.Errorf("[%v] Expecting error. Didn't get one.", data.name)
 				} else {
-
-					ve := err.(*jwt.ValidationError)
+					if errors.As(err, &ve) {
 						// compare the bitfield part of the error
 						if e := ve.Errors; e != data.errors {
 							t.Errorf("[%v] Errors don't match expectation.  %v != %v", data.name, e, data.errors)
@@ -373,6 +374,7 @@ func TestParser_Parse(t *testing.T) {
 						}
 					}
 				}
+			}
 			if data.valid {
 				if token.Signature == "" {
 					t.Errorf("[%v] Signature is left unpopulated after parsing", data.name)